DREDGES

The hydrolift, also called gold dredge and transfer tube, works on the same principle as an airlift, except that water pressure is used instead of air pressure. The tube is rarely more than six feet long and instead of discharging the spill on the surface it discharges it close behind the diver. It is only used when there is very little or no overburden covering a wreck site as much smaller volumes of sediment can be removed when compared to the airlift or prop wash.

A water jet-which consists of nothing more than a hose blowing water out at high pressure-and an air jet, which operates on the same principle, are mainly useful as tools to blow away sediment under a ship’s timbers, in ballast piles or small sand pockets in coral reefs.